Boost converter

ABSTRACT

A boost converter includes an input, an output, a startup circuit, a first switch, a comparator circuit, a switching circuit, a control circuit, a converter circuit, and a switch control circuit. The startup circuit boosts an input voltage up to a first output voltage. The comparator circuit outputs a first signal corresponding to the difference between the output voltage and a first reference voltage. The switching circuit outputs a second voltage based on the first signal. The control circuit outputs a second signal corresponding to the difference between the output voltage and a second reference voltage. The converter circuit boosts the input voltage based on the second signal, and outputs the output voltage. The switch control circuit generates a third signal based on the second signal, and outputs the third signal to the first switch.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2015-176845, filed on Sep. 8, 2015; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a boost converter.

BACKGROUND

A boost converter generally increases a power supply voltage to drive acontrol circuit from an output voltage. When the output voltage is lowerthan a voltage capable of driving the control circuit, however, boostingthe input voltage by using a startup circuit is needed to increases thepower supply voltage capable of driving the control circuit. When thecontrol circuit starts to operate by the startup circuit, the outputvoltage rises. When the output voltage exceeds the voltage capable ofdriving the control circuit, the control circuit starts to operate bythe output voltage. Since the output voltage of the startup circuitbecomes unnecessary at this point, operation of the startup circuit canthen be stopped. Stopping the startup circuit suppresses powerconsumption and raises the efficiency of the whole boost converter.

The input voltage is input to the startup circuit via a switch for thestartup circuit. Using a normally-on-type switch which is in an on-stateeven when a gate does not increase a voltage can make the input voltageinput to the startup circuit. A negative voltage is then necessary toturn off the normally-on-type switch. In a background boost converter,an internal oscillator of the startup circuit is used to apply thenegative voltage. The internal oscillator outputs a voltage oscillatingpositively and negatively around ground potential. The output isrectified and retained. When the control circuit is driven by the outputvoltage, the negative voltage is capable of turning the switch for thestartup circuit off. When the switch for the startup circuit is turnedoff, the startup circuit is stopped by lack of the input voltage.

The negative voltage capable of turning the switch for the startupcircuit off is held by a capacitor. The negative voltage held by thecapacitor may change over time, however, so it is necessary to refreshthe negative voltage. In a background technique, it is necessary todrive the oscillator of the startup circuit for refreshing the negativevoltage held by the capacitor again. Therefore, the oscillator of thestartup circuit consumes electric power, the power consumption of theboost converter increases, and then a problem of a decrease inefficiency of the boost converter arises.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a schematic configuration of a boostconverter according to a first embodiment.

FIG. 2 is a circuit diagram showing a schematic configuration of a boostconverter according to the first embodiment.

FIG. 3 is a block diagram showing a schematic configuration of a boostconverter according to a second embodiment.

FIG. 4 is a block diagram showing a schematic configuration of a boostconverter according to a third embodiment.

FIG. 5 is a block diagram showing a schematic configuration of a boostconverter according to a fourth embodiment.

FIG. 6 is a diagram showing a comparator circuit with hysteresis.

DETAILED DESCRIPTION

The present boost converters are not limited to the embodiments. A boostconverter according to an embodiment described herein includes an input,an output, a startup circuit, a first switch, a comparator circuit, aswitching circuit, a control circuit, a converter circuit, and a switchcontrol circuit. The input that receives an input voltage. The outputthat outputs an output voltage. The startup circuit that boosts theinput voltage up to a first voltage. The first switch connected betweenthe input and the startup circuit. The comparator circuit that receivesas inputs the output voltage and a first reference voltage, and outputsa first signal corresponding to the difference between the outputvoltage and the first reference voltage. The switching circuit thatreceives as inputs the first voltage, the output voltage, and the firstsignal, and outputs the first voltage or the output voltage as a secondvoltage based on the first signal. The control circuit that receives asinputs the output voltage and the second voltage, and outputs a secondsignal corresponding to the difference between the output voltage and asecond reference voltage by using the second voltage as a power source.The converter circuit that receives as inputs the input voltage and thesecond signal, boosts the input voltage based on the second signal, andoutputs the output voltage. The switch control circuit that receives asinputs the first signal and the second signal, determines whether tooutput a third signal for controlling the on-off of the first switchbased on the first signal, generates the third signal based on thesecond signal, and outputs the third signal to the first switch.

Embodiments will now be explained with reference to the accompanyingdrawings.

The First Embodiment

FIG. 1 is a block diagram showing a schematic configuration of a boostconverter according to a first embodiment. The boost converter accordingto this embodiment outputs a predetermined output voltage VOUT from aninput voltage VIN. The boost converter includes an input 1, an output 2,a converter circuit 3, a startup circuit switch (SSW) 4, a startupcircuit 5, a comparator circuit 6, a VDD switching circuit 7, a controlcircuit 8, and a switch control circuit 9.

Each component is explained below.

The input 1 is connected to a DC power supply (not illustrated), andreceives as an input the input voltage VIN. The output 2 is connected toa load (not illustrated), and outputs the output voltage VOUT.

The converter circuit 3 is a circuit converting voltage. The convertercircuit 3 is connected between the input 1 and the output 2. Theconverter circuit 3 outputs the output voltage VOUT from the inputvoltage VIN by turning on and off an internal switch.

The startup circuit switch (SSW) 4 is connected to the input 1 at oneend, and receives as an input the input voltage VIN. When the SSW 4 isturned on, the SSW 4 outputs the input voltage VIN to the startupcircuit 5 connected to it at its other end.

The startup circuit 5 boosts the input voltage VIN, and outputs DCvoltage VST to the VDD switching circuit 7.

The comparator circuit 6 compares the output voltage VOUT with areference voltage VREF input externally, and outputs a comparing resultsignal to the VDD switching circuit 7.

The VDD switching circuit 7 receives as inputs the output voltage VSTfrom the startup circuit 5, the output voltage VOUT, and the comparingresult signal. The VDD switching circuit 7 outputs VST or VOUT to thecontrol circuit 8 based on the comparing result signal.

The control circuit 8 receives as an input VST or VOUT from VDDswitching circuit 7 as a power supply voltage to drive the controlcircuit 8 itself. The control circuit 8 also receives as an input VOUTfrom converter circuit 3 in addition to the power supply voltage. Thecontrol circuit 8 outputs an on-off control signal for switching theinternal switch of the converter circuit 3 to the converter circuit 3 toset the value of the output voltage VOUT to a predetermined value. Theon-off control signal is also output to the switch control circuit 9controlling the on-off of the SSW 4.

The switch control circuit 9 receives as inputs the on-off controlsignal from the control circuit 8 and the comparing result signal fromthe comparator circuit 6. The switch control circuit 9 outputs theon-off control signal for the SSW 4 based on the comparing resultsignal.

At first, the operation of the boost converter, before the outputvoltage VOUT exceeds the reference voltage VREF, is explainedhereinafter. If SSW 4 is turned on, the input voltage VIN is input tothe startup circuit 5, and the startup circuit 5 outputs VST to the VDDswitching circuit 7. The VDD switching circuit 7 receives as inputs theVST and the comparing result signal indicating “VOUT<VREF”. In the caseof “VOUT<VREF”, the VDD switching circuit 7 selects VST, and suppliesthe selected VST to the control circuit 8. The control circuit 8 isdriven by VST, and outputs the on-off control signal to the convertercircuit 3. The converter circuit 3 boosts VIN up to VOUT, and outputsboosted up VOUT.

Next, the operation of the boost converter, after the output voltageVOUT exceeds the reference voltage VREF, is explained hereinafter. WhenVOUT gradually becomes larger and exceeds VREF, the comparator circuit 6outputs the comparing result signal meaning “VOUT>VREF” to the VDDswitching circuit 7 and the switch control circuit 9. When the VDDswitching circuit 7 receives as an input the result signal indicating“VOUT<VREF”, it supplies VST to the control circuit 8, as noted above.When the VDD switching circuit 7 receives as an input the result signalindicating “VOUT>VREF”, however, it supplies VOUT to the control circuit8. When the switch control circuit 9 receives as an input the resultsignal indicating “VOUT>VREF”, it generates a voltage for turning offthe SSW 4 by using the on-off control signal from the control circuit 8,and turns off the SSW 4. For example, the switch control circuit 9includes a switched capacitor circuit 93 (see FIG. 3), and can generatea desired voltage by using the on-off control signal as a clock signal.When the SSW 4 is turned off, the input voltage is not input to thestartup circuit 5, and then the startup circuit 5 stops.

FIG. 2 is a circuit diagram showing a schematic configuration of a boostconverter according to this embodiment. The details of each componentare explained below.

The converter circuit 3 includes an inductor 31, a diode 32, a switch33, and a capacitor 34. The inductor 31 is connected to the input unit 1at one end, and to the diode 32 and the switch 33 at the other end. Theswitch 33 is grounded at one end, and connected to the diode 32 at theother end. The anode of the diode 32 is connected to the inductor 31.The cathode of the diode 32 is connected to the capacitor 34 and theoutput unit 2. The diode 32 can supply the electric current from theinductor 31 to the capacitor 34 and the output unit 2. The capacitor 34is connected to the cathode of the diode 32 and the output unit 2, andgrounded at the other end. The capacitor 34 operates as a smoothingcapacitor. When the switch 33 is turned on and off by the on-off signalfrom the control circuit 8, the input voltage VIN is boosted up to theoutput voltage VOUT.

The startup circuit 5 includes a ring oscillator 51 and a charge pumpcircuit 52. When the startup circuit 5 receives as an input the inputvoltage VIN, the ring oscillator 51 operates and outputs a clock signalCLK. When the charge pump circuit 52 receives as an input the clocksignal CLK, it outputs the DC voltage VST. Instead of the ringoscillator 51, a circuit which can convert a DC voltage to a clocksignal or an AC signal, such as an LC oscillator, may be utilized in thestartup circuit 5. The charge pump circuit 52 may include the switchedcapacitor circuit 93 (of FIG. 3) converting an AC signal such as theclock signal to a DC signal or a rectifier and so on.

The comparator circuit 6 includes a comparator 61. The comparatorcircuit 6 receives as an input the reference voltage VREF and VOUT. WhenVOUT is larger than VREF, the comparing result signal becomes HI (high).When VOUT is smaller than VREF, the comparing result signal becomes LOW.In the case that VOUT is used to the power supply voltage, the comparingresult signal becomes LOW even if the comparator circuit 6 does notreceive as an input the power supply voltage.

The VDD switching circuit 7 includes an inverter 71, a switch 72A, and aswitch 72B. Both the switch 72A and the switch 72B are not in anon-state or off-state at the same time due to the inverter 71. When VOUTis smaller than VREF, the left side switch 72A in FIG. 2 turns on, theright side switch 72B turns off, and VST is supplied as the power supplyvoltage for the control circuit 8. When VOUT is larger than VREF, theleft side switch 72A in FIG. 2 turns off, the right side switch 72Bturns on, and VOUT is supplied as the power supply voltage for thecontrol circuit 8.

The control circuit 8 includes a comparator 81, an oscillator 82, and abuffer 83. The comparator 81 receives as inputs VOUT and a referencevoltage VREFS from internal of the control circuit 8. When VOUT issmaller than VREF, the comparator 81 outputs the signal HI, and theoscillator 82 operates. The oscillator 82 then outputs a clock signal.The clock signal is output to the converter circuit 3 and the switchcontrol circuit 9 via the buffer 83 as the on-off control signal.

The switch control circuit 9 includes a switch 91 and a charge pumpcircuit 92. When the comparing result signal from the comparator circuit6 is HI, the on-off control signal from the control circuit 8 is inputto the charge pump circuit 92. The charge pump circuit 92 generates acontrol signal to turn on and off the SSW 4.

The SSW 4 when applied the off voltage by the control signal for the SSW4 becomes in an off-state. Thus, the input voltage VIN is input to thestartup circuit 5, and then the operation of the startup circuit 5 canbe stopped.

A normally-on-type switch may be used for the SSW 4. Thenormally-on-type switch is a semiconductor switch which is conductive inthe state that no voltage is applied to a gate of the switch. By usingthe normally-on-type switch, the switch SSW 4 is in an on-state if thevoltage applied to the switch control circuit 9 is at ground potential.Thus, even if there is no power supply to drive an internal circuit ofthe boost converter, the input voltage VIN is input to the startupcircuit 5 because the SSW 4 is in an on-state from the beginning.Therefore, SSW 4 can drive the startup circuit 5 without having topreviously drive the switch control circuit 9.

As mentioned above, in this embodiment, the control signal for theconverter circuit 3 output from the control circuit 8 is used for a stopsignal for the SSW 4. Therefore, the power consumption of the startupcircuit 5 can be suppressed by stopping the operation of the startupcircuit 5 until it is necessary to operate. Because of the signal outputfrom the control circuit 8, the startup circuit 5 does not have toprepare a new clock source to turn off the SSW 4. Therefore, powerconsumption can be further suppressed as compared with a backgroundboost converter.

The Second Embodiment

FIG. 3 is a block diagram showing a schematic configuration of a boostconverter according to a second embodiment. The boost converteraccording to this second embodiment has the switched capacitor circuit93 inside the switch control circuit 9. The other configurations are assame as the first embodiment, and their explanation is omitted.

The switched capacitor circuit 93 can adjust a resistance value by theclock signal. Therefore, by using the switched capacitor circuit 93, thevoltage value of the control signal for the SSW 4 output from the switchcontrol circuit 9 can be adjusted to an arbitrary value, such as anegative voltage or a larger voltage than the output voltage, and so on.Thus, it can operate without having to take switching operation of theswitching element used for the SSW 4 into consideration.

As mentioned above, in this second embodiment, the boost converter canoperate even in the case that the switch is a normally-on-type switchrequiring negative voltage to turn off or larger voltage than a voltageof the both ends of the switch. Various switches can be used.

The Third Embodiment

FIG. 4 is a block diagram showing a schematic configuration of a boostconverter according to a third embodiment. The boost converter accordingto this third embodiment has a frequency divider 94 inside the switchcontrol circuit 9. The other configurations are as same as the first andsecond embodiments, and their explanation is omitted.

The frequency divider 94 divides the clock signal input to the switchcontrol circuit 9, that is, a frequency of the on-off control signal.The division ratio can be set to an arbitrary ratio. The operation ofthe charge pump circuit 92 or the switched capacitor circuit 93 in theswitch control circuit 9 can be suppressed. Furthermore, the timing ofturning on and off the SSW 4 and a period for refreshing the off voltagecan be adjusted by dividing. The power consumption of the switch controlcircuit 9 can be suppressed by suppressing the period for refreshing theoff voltage.

As mentioned above, in this third embodiment, the power consumption ofthe switch control circuit 9 can be suppressed by using the frequencydivider 94.

The Fourth Embodiment

FIG. 5 is a block diagram showing a schematic configuration of a boostconverter according to a fourth embodiment. The boost converteraccording to this fourth embodiment includes a comparator circuit 6different from the above embodiments. The other configurations are assame as in the above embodiments, and their explanation is omitted.

The comparator circuit 6 in this fourth embodiment receives as inputsreference voltage VREF1, reference voltage VREF2, and the output voltageVOUT. A comparator with hysteresis 62 (a hysteresis 62) is adopted tothe comparator circuit 6. FIG. 6 is a diagram showing the comparatorcircuit 6 with the hysteresis 62. The hysteresis 62 converts a referencesignal to be compared with an input signal by the value of the previousoutput signal. The input signal is the output voltage VOUT, and thereference signal is the reference voltage VREF1 or the reference voltageVREF2 herein. The voltage VREF1 is larger than the reference voltageVREF2. When the previous comparing result signal is LOW, VREF1 is usedfor the reference signal. When the previous comparing result signal isHI, VREF2 is used for the reference signal.

By comparing the output voltage VOUT with the reference voltage VREF(VREF1 or VREF2) as in the above embodiments, a small fluctuation ofVOUT caused by certain effects like noise may affect the comparingresult. For example, if the difference between VOUT and VREF is verysmall, the plus and minus sign of the difference between VOUT and VREFfrequently fluctuates. In this case, the comparing result signal outputfrom the comparator circuit 6 fluctuates. As a result of this, theswitching operation of the SSW 4 is frequently performed, and then thestartup circuit 5 is frequently driven.

In this fourth embodiment, the reference voltage VREF1 and referencevoltage VREF2 are adopted. Their difference of voltage is an arbitraryvalue. When the previous comparing result signal is LOW (that is, whenthe SSW 4 is off and the operation of the startup circuit 5 is stopped),the startup circuit 5 does not operate unless VOUT is larger than VREF1.Conversely, when the previous comparing result signal is HI (that is,when the SSW 4 is on and the operation of the startup circuit 5 isdriven), the startup circuit 5 does not stop unless VOUT is smaller thanVREF2. Thus, realizing the start-stop condition of the startup circuit 5is harder than the above embodiments, and the operation of the startupcircuit 5 is more stable. Therefore, unnecessary increase of powerconsumption of the startup circuit 5 can be further suppressed, and theefficiency of the boost converter further increases.

As mentioned above, in this fourth embodiment, the power consumption ofthe startup circuit 5 can be even further suppressed.

While certain embodiments have been described, these embodiments havebeen presented by way of examples only, and are not intended to limitthe scope of the inventions. Indeed, the novel embodiments describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A boost converter, comprising: an input thatreceives an input voltage; an output that outputs an output voltage; astartup circuit that boosts the input voltage up to a first voltage; afirst switch connected between the input and the startup circuit; acomparator circuit that receives as inputs the output voltage and afirst reference voltage, and outputs a first signal corresponding to thedifference between the output voltage and the first reference voltage; aswitching circuit that receives as inputs the first voltage, the outputvoltage, and the first signal, and outputs the first voltage or theoutput voltage as a second voltage based on the first signal; a controlcircuit that receives as inputs the output voltage and the secondvoltage, and outputs a second signal corresponding to the differencebetween the output voltage and a second reference voltage by using thesecond voltage as a power source; a converter circuit that receives asinputs the input voltage and the second signal, boosts the input voltagebased on the second signal, and outputs the output voltage; and a switchcontrol circuit that receives as inputs the first signal and the secondsignal, determines whether to output a third signal for controlling theon-off of the first switch based on the first signal, generates thethird signal based on the second signal, and outputs the third signal tothe first switch.
 2. The boost converter according to claim 1, whereinthe converter circuit includes: an inductor connected to the input at afirst end, a second switch grounded at a first end and connected to asecond end of the inductor at a second end, a capacitor connected to theoutput at a first end and grounded at a second end, and a diode whoseanode is connected to the second end of the inductor and whose cathodeis connected to the first end of the capacitor.
 3. The boost converteraccording to claim 1, wherein the first switch includes anormally-on-type switch device that is in an on-state before receivingas an input the third signal.
 4. The boost converter according to claim1, wherein the switch control circuit further includes a switchedcapacitor, and the switched capacitor sets a voltage value of the thirdsignal to a predetermined value based on the second signal.
 5. The boostconverter according to claim 1, wherein the switch control circuitfurther includes a frequency divider, and the frequency divider dividesthe frequency of the second signal to one-Nth (N is an integer of 1 ormore), and generates or outputs the third signal by using the dividedfrequency.
 6. The boost converter according to claim 1, wherein thecomparator circuit further receives as an input a third referencevoltage, selects the second reference voltage or the third referencevoltage based on a feedback signal of the first signal, and outputs anew first signal based on the difference between the second referencevoltage or the third reference voltage and the output voltage.